Dell Dimension E520 @ Dell $959.51
We recently listed a coupon for 3% off at dell (http://www.buckscoop.com.au/deals/4553/3-off-at-dell). So you can go to Dell, get this machine at $998 delivered, take the upgrade to 20" screen work your way through put the coupon code in when prompted and then factor in the cashback from here and the price ends up at $959.51 delivered.
Now if your a bit of a trader and dealer and you want a 20" Dell monitor but dont want to pay the $499 these ones normally retail at, you could pick up the machine and then put it straight onto ebay - brand new - with box and maybe you'll end up with a nice bargain branded monitor.
Basic details for the machine are Intel P4 3.06Ghz, XP Home, 512kb Ram, 80Gb HDD, DVD writer ect.